1. Field of The Invention
The present invention relates generally to a method of coding a digital data signal. Particularly, the invention relates to a digital signal encoding method which can minimize visible error displayed after transmission reception without increasing an information volume overhead associated with the synchronization code and the like.
2. Description of The Related Art
In digital image transmission systems, a digital image signal is generally transmitted in compressed form. When such a compressed digital signal is received, it is expanded to obtain a playback image signal suitable for viewing. At the compression side of the system, a correlation between frames is utilized, generally via interframe coding between the compressed frames. According to this, based on the interframe coding only, when transmission error occurs in the transmission path, error propagation in the direction of time cannot be prevented. For prevention of such error propagation, coding is inserted into the transmission signal at every cycle of a set time period. As well as interframe coding, in frame coding may also be inserted every given time period.
Referring to FIG. 6, an I frame is provided within frame coding while P and B frames are provided with interframe coding. According to this, the content of an I frame before a P frame, or of a P frame only may be predicted, an I or P frame before or after a B frame may be predicted while other frames cannot be predicted.
At this, according to both types of coding, one frame of the digital video signal is divided into a plurality of data sets and each data set is decoded independently of other data sets. In addition, at the head of each data set, a synchronization code is added before transmission. Thus, at the reception side, decoding is carried out according to the unit of the data sets on the basis of the synchronization code.
According to the above system, with interframe coding there is a large disparity in the influence of error on transmission depending on the location of the error. For example, referring again to FIG. 6, if error occurs in an I frame, the influence thereof will affect all intermediate frames until the next I frame. If error occurs in a P frame, the influence thereof will affect the preceding two B frames and the frames after the P frame, while error occuring in a B frame will not influence other frames. In addition, transmission error occuring in a frame coded with in frame coding has the most visible influence.
Also, such error will be visibly manifest on a a display screen displaying the digital video signal, from the location of the error until the detection of the subsequent synchronization code. In such case in order to minimize the effect of the error, it is necessary to increase the number of data sets per frame, this however, reduces a surface area of each data set. According to this, the information volume overhead, of the synchronization code, etc., is increased. However, according to such increase, overall image quality is degraded.
Thus it has been required to provide a coding system for a digital video signal which may minimize visible error displayed after reception without increasing an information volume of overhead associated with the synchronization code and the like.